1. Field of the Invention
The present invention relates to aluminum gallium nitride/gallium nitride (AlGaN/GaN) high-electron mobility devices for use in high-power, high-frequency device applications, and more particularly to the control or compensation of charge within the channel of such high-electron mobility devices.
2. Background
The aluminum gallium nitride/gallium nitride hetero-interface or heterojunction creates a planar region of high charge and high mobility electrons called a two-dimensional electron gas (2DEG), and is commonly used in high-electron mobility devices. However, typical performance problems with gallium nitride based high-electron mobility devices include dispersion related to unintentional traps in the nominally undoped or intrinsic gallium nitride buffer layer. These traps result in reduced channel charge in the two dimensional electron gas, current slump during device operation and reduced device lifetimes, among other problems. Also, AlGaN/GaN high-electron mobility devices are planar growth structures that are typically depletion-mode devices that are normally-ON in their unbiased state, so that electrical current flows between source and drain contacts even when voltage is not applied to a corresponding gate contact. For electrical power switching applications, normally-OFF or enhancement-mode devices are preferable, such that charge does not flow between source and drain contacts in absence of applied voltage to the corresponding gate contact. Thus, there is a need to provide high-electron mobility devices having improved performance, and also normally-OFF high-electron mobility devices having improved performance.